Doris Preininger

Many species reproduce by participating in explosive breeding events, where hundreds of individuals converge at specific locations for a short time period to mate. During these spectacular aggregations, many males must actively search and compete for a limited number of females. One idea is that sexual selection in explosive breeding species favors the evolution of communication strategies facilitating easy detection of males and females. As such, the emergence of dynamic sexual dichromatism, a reversible change of body coloration of one sex, might act as a visual signal promoting rapid mate recognition in dense breeding aggregations. We tested this idea in Asian Common Toads (Duttaphrynus melanostictus), an explosive breeder in which males quickly turn from brown to bright yellow for up to two days during mating. Thus, we first explored whether color differences of brown and yellow are sufficient to be perceived and distinguished by toads using a color vision model. In a set of behavioral experiments, we then tested the interactions of male toads with a yellow (resembling a breeding male) and a brown (resembling a female) 3D model toad to determine the functional significance of yellow male coloration during mating. Finally, we compared male body color, morphological parameters, and body condition of mated and non-mated males to investigate if these traits are influenced by securing a mate or female mate choice. Our results show that dynamic yellow coloration displayed by males can be easily discriminated against brown female conspecifics from a toad's point of view. During model experiments, males had twice as much physical contact with brown models and clasped them 40 times more often than yellow models. Coloration and several morphological traits did not differ between mated and non-mated males; hence, securing a mating partner was not influenced by variations in color or morphology. Our study supports the idea that dynamic sexual dichromatism repeatedly evolved as a visual signal mediating fast mate recognition in tropical and temperate anuran species solving a common problem in time-limited, dense breeding aggregations, by minimizing same-sex harassment and mismatch.

The European Union of Aquarium Curators (EUAC) boasts a membership of 150 dedicated individuals, standing as a vital cornerstone within the European public aquarium community. Since 2004, the EUAC Conservation Fund has granted over a quarter of a million euros to approximately 50 conservation projects spanning the globe. These initiatives, diverse in nature and scale, have yielded tangible impacts on local populations and their focal species. This paper delves into the outcomes of these conservation endeavors and proposes enhancements to ensure that the funding is unequivocally channeled towards conservation efforts. One resounding observation gleaned from the array of projects spotlighted in this study is the profound community engagement that emerges, irrespective of the final project outcomes. These endeavors serve as a catalyst for local communities, shedding light on subjects that would otherwise remain shrouded in obscurity. Furthermore, the EUAC-backed projects illuminate the expansive reach of public aquarium initiatives, transcending the confines of acrylic tank walls and institutional boundaries to resonate globally, heightening local awareness about the imperative to safeguard biodiversity. These findings underscore a prospective trajectory for both the EUAC and the public aquaria it comprises: an intensified advocacy and collaboration with legislative bodies to fortify in situ conservation measures. In essence, it is imperative that the public comprehends the pivotal role played by aquaria in preserving a multitude of species and acknowledges that their visits directly contribute to funding projects aimed at safeguarding species within their natural habitats.

Zhao et al. recently reported results which, they claim, suggest that sexual selection produces the multimodal displays seen in little torrent frogs (Amolops torrentis) by co-opting limb movements that originally evolved to support parasite defense (Zhao et al., 2022). Here, we explain why we believe this conclusion to be premature.

Morphological differences between males and females are common among reptiles. A particularly interesting sexually dimorphic feature whose function is largely unknown is the number and pattern of specific scales. Several lizard species possess an arrangement of centered scales near the cloacal region that differ between the sexes and can be used for sex determination. The presence of postcloacal buttons, sexually dimorphic postcloacal scales on both sides of the body, is an exclusive trait in the subfamily Tupinambinae and is only poorly documented. Here, we investigate postcloacal scales in northern caiman lizards (Dracaena guianensis) housed at the Vienna Zoo. For a period of two years, we documented scale patterns and performed morphometric measurements of individuals of different age classes. Caiman lizards were CT scanned to confirm the sexes. Males exhibit three raised postcloacal scales in a row behind the left and right leg, while females possess one or two large scales surrounded by several smaller scales. The study provides the first evidence that these scales can function as a reliable trait to distinguish the sexes regardless of age or reproductive status. The sexually dimorphic bilateral scale pattern is present immediately after hatching and does not change during development. Scales only increase in thickness and length during growth. We further demonstrate that sexual size dimorphism (SSD) exists in juveniles during ontogenetic development. Juvenile females had a larger SVL, body length, tail length and higher weight compared to juvenile males. This SSD could not be confirmed in adults, and sex determination based on SSD seems unreliable.

A diversity of defence colourations that shift over time provides protection against natural enemies. Adaptations for camouflage depend on an organism’s interactions with the natural environment (predators, habitat), which can change ontogenetically. Wallace’s flying frogs (Rhacophorus nigropalmatus) are cryptic emerald green in their adult life stage, but juveniles are bright red and develop white spots on their back 1 month after metamorphosis. This latter conspicuous visual appearance might function as antipredator strategy, where frogs masquerade as bird or bat droppings so that predators misidentified them as inedible objects. To test this idea, we created different paraffin wax frog models—red with white spots, red without white spots, green, and unpainted—and placed them in equal numbers within a > 800 m² rainforest house at the Vienna Zoo. This environment closely resembles the Bornean rainforest and includes several free-living avian predators of frogs. We observed an overall hit rate of 15.5%. A visual model showed that the contrast of red, green and control models against the background colouration could be discriminated by avian predators, whereas green models had less chromatic difference than red morphs. The attack rate was significantly greater for red but was reduced by half when red models had white spots. The data therefore supports the hypothesis that the juvenile colouration likely acts as a masquerade strategy, disguising frogs as animal droppings which provides similar protection as the cryptic green adult colour. We discuss the ontogenetic colour change as a possible antipredator strategy in relation to the different habitats used at different life stages. Significance statement: Predation pressure and the evolution of antipredator strategies site at the cornerstone of animal-behaviour research. Effective antipredator strategies can change in response to different habitats that animals use during different life stages. We study ontogenetic shifts in colour change as dynamic antipredator strategy in juvenile and adult Wallace’s flying frogs. We show that the unusual colour pattern of juveniles (bright red with small white spots) likely functions as a masquerade of animal droppings. Specifically, we show that white dotting, which can be associated with animal faeces, acts as the main visual feature that turns an otherwise highly conspicuous individual into a surprisingly camouflaged one. To our knowledge, this is the first experimental exploration of a vertebrate masquerading as animal droppings.

The European Union of Aquarium Curators (EUAC) includes 150 members and is an important association for the European public aquarium community. Since 2004, over one quarter of a million euros were awarded by the EUAC Conservation Fund to approximately 50 projects, which spanned across the globe. While projects varied greatly in content and scope, several achieved a significant impact in local populations and/or their focus species. This paper reports on results achieved by these conservation efforts and what improvements can be made, to ensure that the funding is indeed invested in conservation efforts per se. Perhaps the most valid conclusion to be drawn from the list of projects covered in this work is the fact that, regardless of the outcome, as far as preservation of the species are concerned, local communities were actively engaged in a subject that would, otherwise, remain unknown to them. Additionally, these EUAC funded projects highlight how public aquarium activities reach far beyond the acrylic panels surrounding the tanks and indeed the walls of the institution, as they spread around the world and raise awareness within local communities to preserve biodiversity. These results further suggest that a future direction for EUAC, as well as the public aquaria it consists of, could – indeed should - include more strenuous lobbying with legislating bodies, to ensure more adequate – and stronger – in situ conservation measures. In conclusion, with so many doubts being raised by different movements about the existence of aquaria and zoos, it is important that the public is aware that it is their visit to see the ambassadors of different species of animals that supports the funding of many of these pilot projects that aim to preserve species in their natural environment.

Camera traps are very useful tools in determining the presence/absence of rare and cryptic species while shedding light on behavioral traits. Passive infrared triggered cameras are routinely used in homeothermic animals, but in ectothermic reptiles, this surveillance method has proven highly unreliable. As part of the conservation goal to provide better understanding and protection for the critically endangered freshwater turtle Batagur baska, we investigated their largely unknown nesting behavior and tested video-based motion detection by comparing 2 different camera-trapping systems and their settings under controlled conditions at the Vienna Zoo. A pixel-based video surveillance camera was superior to a camera trap with motion sensor. The surveillance camera allowed reliable motion detection at sensitive settings, and video capture precision could be enhanced by marking the terrapin with reflective tape. This video surveillance camera was then deployed over 2 breeding seasons (2019 and 2020) in the conservation breeding project of the northern river terrapin (B. baska, Gray 1830) in Bhawal National Park in Bangladesh. Analysis of video recording demonstrated for the first time that female northern river terrapins nested on average for a period of 1.5 hrs and produced a single clutch per year. Results indicate that females inspect sandbanks and visit suitable nesting sites several times before egg deposition, suggesting that nest-site selection is not random in B. baska. In addition, water temperature measurements of the breeding ponds in 2 captive breeding sites of the B. baska project showed an annual average temperature decrease to 168C–188C during the mating season and an average increase to 288C–318C before the nesting season. Temperatures on nesting nights vary between the 2 breeding sites and differ between nesting events within each site, suggesting that overall seasonal temperature shifts initiate the nesting periods, while other physiological and environmental factors might trigger the actual nesting event. With the help of consistent motion-triggered video recording, our study provides a first underpinning of the nesting ecology of B. baska.

The external morphology of two molecularly identified tadpoles of the genus Staurois, S. parvus and S. tuberilinguis is described. These tadpoles display a typical fossorial morphology characterized by a strongly depressed body, small subcutaneous eyes, a vermiform appearance with a long tail and reduced fins, a nearly pigmentless skin, a KRF of 1:1+1 on the upper labium and numerous keratodont rows on the lower one. The two species can be distinguished by several morphological differences, the most conspicuous are the eye condition (not bulging and covered by skin in S. tuberilinguis) and the presence of numerous white isolated acini on the body and tail in S. parvus. These differences support the specific status of S. parvus relatively to S. tuberilinguis despite low genetic divergence between these two taxa. The morphology of these tadpoles, as well as the buccopharyngeal anatomy of S. parvus, are compared to those of the tadpoles in the family Centrolenidae and the definition of the fossorial ecomorphological guild is updated.